Embraer S A EMB-505 N304QS and Boeing 737 823 N896NN incident near Dallas, Texas

Probable cause

The controller's miscommunication of a clearance and failure to recognize and correct the readback resulting in the flight crew initiating takeoff without a clearance.

NTSB analysis

This runway incursion resulted from communications errors. The local control east controller (LE1) misspoke when intending to issue a landing clearance for a flight on approach to runway 35C and instead issued the flight on approach a takeoff clearance from runway 35L. The pilot of AAL2408, already in line up and wait position on runway 35L, interpreted the communication to be a takeoff clearance for his flight, acknowledged the takeoff clearance, and initiated takeoff.

Immediately prior to AAL2408 initiating takeoff roll, the LE1 controller had cleared three different aircraft to cross runway 35L on three different taxiways. As AAL2408 began its takeoff roll the Runway Status Lights (RWSLs) on runway 35L activated Activation of the RWSL illuminated the Runway Entrance Lights (RELs) at the hold short locations of the three aircraft that had just been instructed to cross runway 35L and illuminated the Takeoff Hold Lights (THLs) at the approach end of the runway. The RELs provided a visual signal to the pilots holding short of runway 35L indicating the runway was unsafe to enter or cross. The THLs provided a visual signal to the pilot of AAL2408 that the runway was occupied however, data indicate that AAL2408 had progressed too far down the runway to observe the THLs by the time they had illuminated. Of the three aircraft holding short of runway 35L, only one proceeded across runway 35L. As that aircraft cleared the runway at taxiway K8 the Airport Surface Detection Equipment, Model-X indicated AAL2408's speed to be 120 knots and the closest proximity between the two aircraft was approximately 2,800 feet.

In this incident, the LE1 controller adjusted his speech rate to the traffic volume while attempting to comply with the requirements of issuing explicit runway crossing clearances for each runway that intersects a taxi route resulting in an excessive speech rate by the LE1. During a System Service Review after the event, controllers identified a recent procedural change that required additional verbiage when issuing crossing instructions, and an increased speech rate associated with increased workload.

Text from the NTSB. Open the NTSB docket for OPS16IA008 for the full record.